Each fasciculus consists in turn of approximately 100 to 150 individual muscle fibers that range from 1 to 40 micrometers in length and 10 micrometers in dimeter.
A muscle fiber comprises a number of long, thin, cylindrical rods known as myofibrils, the essential contractile units of muscle, which are separated from one another by a highlight specialized network of tubules the sarcoplasmic reticulum.
The sarcoplasmic reticulum, a specialized organelle that’s stores and releases calcium, is an interconnecting network of tubules running parallel with and wrapped around the myofibrils.
The major significant of the sarcoplasmic reticulum is its ability to store, release and take up calcium and thereby control muscle contraction.
Myofibrils are bathed in an aqueous fluid (sarcoplasm), which is about 75-80% water and contains mitochondria, enzymes, glycogen, adenosine triphosphate, creatine, phosphate and myoglobin.
Myofibrils range in diameter from 1 to 2 micrometers. They are grouped in clusters and run the length of the muscle fiber. In turn each myofibril comprises long, thin strands of serially linked sarcomeres. Sarcomeres are the functional unit of a muscle.
Myofibrils in muscle fiber
